U.S. Pat. No. 8,829,406 to Akerman, whose disclosure is incorporated herein by reference, describes optical apparatus that includes a device package, with a radiation source contained in the package and configured to emit a beam of coherent radiation. A diffractive optical element (DOE) is mounted in the package so as to receive and diffract the radiation from the radiation source into a predefined pattern comprising multiple diffraction orders. An optical detector is positioned in the package so as to receive and sense an intensity of a selected diffraction order of the DOE.
U.S. Pat. No. 3,997,715 to Elliot, whose disclosure is incorporated herein by reference, describes a focus detector that includes apertured photodetectors which intercept a radiant beam. Changes in focus differentially affect the amount of radiation impinging on the detectors resulting in corresponding changes in their signal output. A videodisc system employing the detector moves a focusing lens to compensate for variations in the position of a target videodisc, so that a scanning beam is always accurately transmitted to a detector. A difference circuit connected to two photodetectors generates a driving signal to energize a lens-moving motor for shifting the focusing lens toward or away from the videodisc.
U.S. Pat. No. 6,862,076 to Mulder, whose disclosure is incorporated herein by reference, presents a system and method for determining the stray radiation condition of a projection system. The invention includes providing a detector with a detector aperture coincident with the image plane of the projection system, measuring a reference parameter in accordance with the projection beam intensity, measuring a stray radiation parameter of an image of an isolated feature and calculating a coefficient representative of the stray radiation condition of the projection system based on the measured stray radiation parameter and the reference parameter. The extent of the detector aperture fits within the extent of a notional shape, which is defined by first scaling down the shape of the feature and subsequently displacing each line element constituting the edge of the scaled down shape, parallel to itself, over a distance of at least lambda/NA in a direction perpendicular to that line element.
U.S. Pat. No. 4,762,993 to Moses, whose disclosure is incorporated herein by reference, describes a method and apparatus for sensing the deviation of a neutral particle beam from a predetermined direction. The neutral particle beam is derived from a composite particle beam having residual charged particles with substantially the same directional characteristics as the neutral particles making up the neutral particle beam. A deflection magnet deflects at least a portion of the charged particles from the composite particle beam a known amount toward a detector array including apertures for forming a plurality of charged particle beamlets. Deviation of the charged particle beamlet is determined as an indication of the direction of the neutral particle beam relative to the predetermined direction. A similar measurement of neutral particles around the periphery of the neutral beam provides deviation data of the neutral beam which, when correlated with the data of the charged particle beam, provide an instantaneous transfer characteristic of the magnetic deflection system.
U.S. Pat. No. 5,481,109 to Ninomiya, whose disclosure is incorporated herein by reference, describes a surface analysis method and an apparatus for carrying out the same in which the method involves the detection of fluorescence X-rays emitted from the surface of a sample in response to a finely focused electron beam irradiated thereto, whereby residues on the sample surface are analyzed qualitatively and quantitatively. An electron beam (1) is irradiated through a hole (9) at the center of an X-ray detector (8) into a fine hole (h) on the surface of a sample (2). In response, fluorescence X-rays are emitted from inside the fine hole (h) and are detected by an annular X-ray detector (8) having an energy analysis function near the axis of the electron beam (1) (preferably within 20 degrees with respect to the center axis of the electron beam). This arrangement allows the fluorescence X-rays from the fine hole (h) to reach the X-ray detector (8) without being absorbed by the substance of the material. That in turn ensures qualitative and quantitative analysis of high accuracy about residues in fine holes of large aspect ratios. Since the method is of non-destructive nature, the analyzed sample may be placed unscathed back into the fabrication process.
U.S. Pat. No. 5,937,026 to Satoh, whose disclosure is incorporated herein by reference, provides a structure wherein a detector for measuring the fluorescent X-rays is made into a thin and hollow cylindrical type configuration and this detector is fitted onto the vicinity of an end on the sample side of the X-ray capillary tube for decreasing primary X-rays to a thin flux.